The biosynthesis of acarbose and validamycin

The studies reported here have established the biosynthetic origin of the mC7N units of acarbose and validamycin from sedo-heptulose 7-phosphate, and have identified 2-epi-5-epi-valiolone as the initial cyclization product. The deoxyhexose moiety of acarbose arises from glucose with deoxythymidyl-diphospho-4-keto-6-deoxy-D-glucose (dTDP-4-keto-6-deoxy-D-glucose) as a proximate intermediate. However, despite the identical origin of the aminocyclitol moieties in acarbose and validamycin A, the pathways of their formation seem to be substantially different. Validamycin A formation involves a number of discrete ketocyclitol intermediates, 5-epi-valiolone, valienone, and validone, whereas no free intermediates have been identified on the pathway from 2-epi-5-epi-valiolone to the pseudodisaccharide moiety of acarbose. The stage is now set for unraveling the mechanism or mechanisms by which the two components of the pseudodisaccharide moieties of acarbose and validamycin are uniquely coupled to each other via a nitrogen bridge.     

Anti-infective potential of caffeic acid and epicatechin 3-gallate isolated from methanol extract of Euphorbia hirta (L.) against Pseudomonas aeruginosa

Euphorbia hirta (L.) plant is traditionally used in Malaysia for the treatment of gastrointestinal, bronchial and respiratory ailments caused by nosocomial infectious agents. Bioactivity-guided fractionation of the methanol extract of the aerial parts of E. hirta and analysis using high-performance liquid chromatography have led to the isolation of two antibacterial compounds. These compounds were identified as caffeic acid (CA) and (–)-epicatechin 3-gallate (ECG) based on spectroscopic analyses and comparison with previously published data. Using broth microdilution method, both ECG and CA had demonstrated significant minimum inhibitory concentration of 15.6 and 31.3 μg/mL respectively, against Pseudomonas aeruginosa. Time-kill assessment of ECG and CA displayed bactericidal effect on P. aeruginosa cells.     

Synthesis,characterization and study of antibacterial activity of enaminone complexes of zinc and iron

Complexes of enaminones; 4-N,N-diethylamine-pent-3-ene-2-one [HL¹], 4-N,N-di n-propylamine-pent-3-ene-2-one [HL²] and 4-N,N-dicyclohexylamine-pent-3-ene-2-one [HL³] with Fe(II) and Zn(II) ions were prepared by reacting the equimolar ethanolic solutions of the ligands (HL¹, HL² and HL³) with ethanolic metal solutions. The complexes formed, were characterized by infrared, ultraviolet and atomic absorption spectroscopy. Ligands and their metal complexes were tested against Escherichia coli and Staphylococcus aureus bacteria to assess their antibacterial action using disc diffusion method. Ligands were completely inactive against bacteria whereas the complex Zn (HL¹) has significant action on both bacteria, indicating that it has a good potential as bactericide. Other complexes have normal antiseptic character.     

Amperometric determination of live <Emphasis Type="Italic">Escherichia coli</Emphasis> using antibody-coated paramagnetic beads

Detecting and enumerating fecal coliforms, especially Escherichia coli, as indicators of fecal contamination, are essential for the quality control of supplied and recreational waters. We have developed a sensitive, inexpensive, and small-volume amperometric detection method for E. coli -galactosidase by bead-based immunoassay. The technique uses biotin-labeled capture antibodies (Ab) immobilized on paramagnetic microbeads that have been functionalized with streptavidin (bead–Ab). The bead–Ab conjugate captures E. coli from solution. The captured E. coli is incubated in Luria Bertani (LB) broth medium with the added inducer isopropyl -D-thiogalactopyranoside (IPTG). The induced -galactosidase converts p-aminophenyl -D-galactopyranoside (PAPG) into p-aminophenol (PAP), which is measured by amperometry using a gold rotating disc electrode. A good linear correlation (R²=0.989) was obtained between log cfu mL^–1 E. coli and the time necessary to product a specific concentration of PAP. Amperometric detection enabled determination of 2×10⁶ cfu mL^–1 E. coli within a 30 min incubation period, and the total analysis time was less than 1 h. It was also possible to determine as few as 20 cfu mL^–1 E. coli under optimized conditions within 6–7 h. This process may be easily adapted as an automated portable bioanalytical device for the rapid detection of live E. coli.     

Total absorption spectroscopy of the β-delayed proton emitter 117Ba

The very neutron-deficient ¹¹⁷Ba nuclei were produced in ⁵⁸Ni-induced reactions on a ⁶³Cu target and selected for spectroscopic studies by using BaF⁺ molecules formed in the ion source of the GSI on-line mass separator. The -decay of ¹¹⁷Ba was investigated by means of the total absorption -ray spectrometer and a telescope for -delayed particle detection. In the analysis combining the -delayed -ray and proton data the energy window available for -delayed proton emission, the branching ratios for proton transitions to the ¹¹⁶Xe levels and the -feeding of the -ray and proton-emitting ¹¹⁷Cs states were determined. The -strength function for ¹¹⁷Ba derived from the measured -feeding distribution revealed the existence of a broad resonance structure at ¹¹⁷Cs excitation energy of about 4-5 MeV. The results of the -delayed proton studies and -strength measurements are confronted with theoretical predictions.     

Magnetocaloric effects in Ni-Mn-X based Heusler alloys with X=Ga, Sb, In

The Mn-based Heusler alloys encompass a rich collection of useful materials from highly spin-polarized systems to shape memory alloys to magnetocaloric materials. In this work we have summarized our studies of magnetostructural transitions from paramagnetic austenite to ferromagnetic martesite phases at TMC in Ni₂MnGa-based alloys (Ni₂Mn_0.75Cu_0.25-xCo_xGa, Ni₂Mn_0.70Cu_0.30Ga_0.95Ge_0.05, Ni₂Mn_1-xCu_xGa, Ni_2+xMn_1-xGa, and Ni₂Mn_0.75-xCu_xGa), and martensitic transitions from the ferromagnetic austenite to the martesite state in off-stoichiometric Ni-Mn-(In/Sb) Heusler alloys. The phase transition temperatures and respective magnetic entropy changes (ΔS) depend on composition in these systems and have been determined from magnetization measurements in the temperature interval 5-400 K, and in magnetic fields up to 5 T. It is shown that, depending on the composition and doping scheme the “giant” ΔS=40-60 J/(kgK) (for a field change of 5 T) can be observed in the temperature range (300-360 K) for the Ga-based alloys. The interplay between or coupling of the various transitions in Ni₂Mn(Mn,X) systems with X=Sb and In leads to exchange bias effects, giant magnetoresistance, and both inverse and “normal” magnetocaloric effects.     

Growth and characterization of ZnO multipods on functional surfaces with different sizes and shapes of Ag particles

Three-dimensional ZnO multipods are successfully synthesized on functional substrates using the vapor transport method in a quartz tube. The functional surfaces, which include two different distributions of Ag nanoparticles and a layer of commercial Ag nanowires, are coated onto silicon substrates before the growth of ZnO nanostructures. The structures and morphologies of the ZnO/Ag heterostructures are investigated using X-ray diffraction and field emission scanning electron microscopy. The sizes and shapes of the Ag particles affect the growth rates and initial nucleations of the ZnO structures, resulting in different numbers and shapes of multipods. They also influence the orientation and growth quality of the rods. The optical properties are studied by photoluminescence, UV-vis, and Raman spectroscopy. The results indicate that the surface plasmon resonance strongly depends on the sizes and shapes of the Ag particles.     

New results on proton emission from odd-odd nuclei

⁷⁸Kr beams were used to bombard ⁵⁸Ni, ⁹²Mo and ⁹⁶Ru, producing three new, odd-odd, proton-emitting isotopes, ¹³⁰Eu, ^164mIr and ¹⁷⁰Au. Preliminary experimental and theoretical results will be presented in this paper. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: mahmud@ph.ed.ac.uk     

Microstructure holey fibers as wideband dispersion compensating media for high speed transmission system

This paper presents a dispersion compensating microstructure holey fiber for wideband transmission system. The finite element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. According to simulation, negative dispersion coefficient of −1455 ps/(nm km) and a relative dispersion slope (RDS) close to that of single mode fiber of about 0.0036 nm⁻¹ is obtained at 1.55 μm. The variation of structural parameters is also studied to evaluate the tolerance of the fabrication. The proposed module can be used in 40 Gb/s dense wavelength division multiplexing (DWDM) systems in optical fiber communication networks.     

Transient characteristics of the InGaP–GaAs–InGaAs–GaAs transistor laser

Transient characteristics of the InGaP–GaAs–InGaAs (quantum well)-GaAs transistor laser are studied. Rate equations are numerically solved to obtain the response of current density and photon density. Expression of resonance frequency $f_{r}$ is obtained by solving the rate equations analytically. It has been found that the $f_{r}$ increases with decreasing spontaneous carrier lifetime and with increasing value of the bias current density.